Conventionally, there has been a method known as a plasma assist method by which a chemical reaction of a deposition material is accelerated due to plasma generated in a chamber at the time of deposition. In the plasma assist method, the plasma is normally formed by a plasma gun which injects a discharge gas to form the plasma while emitting electrons to ionize the discharge gas.
In general, the plasma gun includes a converging coil for forming a magnetic flux to guide the emitted electrons. When the converging coil is provided, the electrons emitted from the plasma gun move while winding around a magnetic field formed by the converging coil, so that the plasma can reach a position far from the plasma gun.
However, even when the converging coil is used, a range of the plasma that the plasma gun can form is limited. Therefore, in a case where a deposition target body is large on which a deposition target film is to be formed, there is a need to oppositely arrange two plasma guns to form plasma over a wide range as disclosed in Patent Document 1, for example.
FIG. 3 shows a deposition apparatus in which plasma guns 22 are oppositely arranged on both sides of a chamber 21. The plasma gun 22 is a pressure-gradient type plasma gun and includes a cathode 23 for emitting electrons, a first electrode 24 and a second electrode 25 for forming voltage gradients, a feedback electrode 26 for collecting the electrons, and a converging coil 27 for forming a magnetic flux to guide the electrons. Thus, a discharge gas is injected so as to penetrate centers of those components.
In this deposition apparatus, the magnetic fluxes formed by the converging coils 27 in the opposed plasma guns 22 repel each other. The electrons emitted from the plasma gun 22 travel while winding around the magnetic flux formed by the converging coil 27, so that they turn back along the repelling magnetic flux and return to each feedback electrode 26 as shown by dotted lines in the drawing. Therefore, the electrons are not sufficiently supplied to an intermediate position of the opposed plasma guns 22, and the plasma is low in density at the position, so that an imbalanced discharge region P is formed as shown in the drawing.
Therefore, in a case where the deposition is performed for a large-size panel, a chemical reaction is not sufficiently caused in the center portion because the plasma is low in density there, so that the problem is that a deposition target film is not uniformly formed because the film is poor in adhesiveness or the like.